The Great Barrier Reef off the northeastern coast of Australia (Kyodo).
The full extent of Great Barrier Reef coral bleaching is difficult to determine because of workplace health and safety.
Coral descends as far as 70 meters in some parts of the Great Barrier Reef but safety regulations mean scuba diving scientists only frequently explore the top 10 to 12 meters of the reef.
That's not a particular problem because shallow reefs are socially and economically more important anyway, Marine Park Authority chief scientist David Wachenfeld told a parliamentary inquiry on Monday.
Shallower reefs are more productive and biologically diverse, and fishing for coal trout is constrained to smaller depths.
"Tourists don't dive on coral at 50 meters - tourists go in glass bottom boats and snorkel and so the vast majority of the very great economic value of the reef is based on the shallow corals," he said.
Autonomous vehicles are used to collect information on deeper coral, and Dr Wachenfeld believes as technology improves scientists will get a better picture of what's happening further below.
The latest reef data, including the effects of Cyclone Debbie, will be released in the coming weeks.
Scientists will begin to look at the impact of wet season flooding in June.
© AAP 2018